1. Field of the Invention
This invention relates to an energy feeding device for a microwave heating appliance. In accordance with this invention there is provided an improved rotary antenna for feeding high-frequency electromagnetic energy into a heating chamber which is stable in quality and in performance, and which does not cause sparking even though it comprises a thin-walled metallic pipe for weight reduction purposes.
2. Brief Description of the Prior Art
A conventional antenna of the above-mentioned type comprises a hollow metal pipe which is connected with a revolving drive shaft made of low-loss dielectric material in order to prolong its rotation life and to reduce the size and cost of the drive source, e.g. a motor.
However, such an antenna, made of a thin-walled metal pipe, has a sharp edge at the end which is inserted into a waveguide. Even though a substantial electric field is available near the antenna, the electric field is concentrated around the sharp edge of the pipe. This leads to local sparking under operating conditions involving a large reflection coefficient, such as light loading, resulting in not only the operation being rendered unstable but also the sparking which is continuous, tends to damage the antenna. The above problems are substantially solved by this invention.